This invention relates to hypodermic syringes for withdrawing blood or infusing a patient with serums and the like and, more particularly, to a hypodermic syringe designed to prevent accidental pricking of the fingers or hands of the person using the syringe.
With conventional hypodermic syringes, the administration of an injection or blood withdrawal involves the removal of a protective cap covering the needle of the syringe and, after the withdrawal of the needle from the body of a patient, the replacement of the cap over the needle before the needle is discarded. The procedures just described can easily lead to the accidental pricking of a hand or finger of the administrant, the injection of harmful viruses and bacteria under the skin, and the resultant infection of the administrant. In view of the increasing occurrence of fatal diseases such as Acquired Immune Deficiency Syndrome (AIDS), it is absolutely essential that accidental needle pricks be avoided.
Accidental pricking occurs most often during the removal and replacing of the needle cap. It is at these moments that the hand of the administrant is nearest to the sharp needle point. More specifically, the most common accidental pricking occurs because the cap is firmly held in place over the needle by friction between the cap and a hub in which the needle is mounted. A large frictional force is intentionally provided, such as by the engagement of ribs formed on an external surface of the needle hub and on an internal surface of the cap, so that the cap does not inadvertently become dislodged from the needle and thereby cause the previously sterile needle to become contaminated. In order to overcome the frictional resistance, the administrant must firmly grasp the cap and pull. The release of the cap from the needle hub occurs suddenly, so that there is a tendency for the hand to whip back towards the exposed needle, causing an accidental prick to occur. Accidental pricking also occurs when the cap is being replaced over the needle, since the opening in the cap into which the needle must be inserted is quite small. As a result, a slight misjudgment or unsteadiness causes the needle, instead of entering the small cap opening, to miss the opening and prick the finger of the administrant, which, by virtue of holding the cap, must of necessity be near the cap opening. In fact, such accidental pricking occurs even though caps of excessive length are used to cover even a short needle in an effort to increase the distance between the needle and the administrant's hand. For example, a cap used to cover a 11/2 inch long needle may be as much as 2 inches long.
U.S. Pat. No. 4,842,587, issued on June 27, 1989 to the present inventor, describes a hypodermic needle assembly which overcomes the problems of accidental pricking in the removal and replacement of the needle caps. In the assembly of the application, a cap is incorporated as an integral part of the hypodermic unit, so that the cap requires no removal or replacement. The cap is slidably mounted on formations projecting from a hub in which the needle is mounted. The projecting formations include flaps projecting radially from the hub and resilient bands extending arcuately in one direction from the flaps to contact and guide the cap, maintaining the longitudinal axis of the cap in substantial alignment with the longitudinal axis of a syringe needle. As a result, any danger of the needle piercing a sidewall of the cap, especially during the sliding of the cap, is avoided. The cap has a diameter larger than the diameter of the syringe and a proximal end which is open to permit the cap to move down over the syringe and slide on the arcuate resilient bands. An opposite end of the cap is closed in the sense that there is no opening large enough for a finger to enter and come into contact with the needle. There is, however, an opening large enough for the needle to pass through to reach an exposed position in which an injection or withdrawal can be administered.
In one embodiment disclosed in the aforesaid patent, the cap is retained in the extended position by the engagement of the resilient bands with an annular interference bead on the inner surface of the cap, spaced from the proximal end of the cap, and the separation of the cap from the needle and the needle hub is prevented by the engagement of the resilient bands with an annular stop bead on the inner surface of the cap adjacent the proximal end. In addition, elongate axial ribs on the interior surface of the cap are received in gaps provided between the flaps and adjacent free ends of the arcuate resilient bands. Rotation of the cap causes the elongate ribs to push the bands and, thereby, rotate the needle hub to screw it onto the barrel of the syringe.
U.S. Pat. No. 4,816,022, issued on Mar. 28, 1989 to the present inventor, discloses a hypodermic syringe with a sliding cap which is an improvement in that disclosed in the aforesaid embodiment of U.S. Pat. No. 4,842,587 in that it reduces the chances of the cap being accidentally slid to a position to expose the needle and also facilitates molding the needle hub to provide a more uniform frictional force between the resilient bands and the interior wall of the cap. In accordance with the improvement, the annular stop bead on the inner surface of the cap, instead of being adjacent to the proximal end of the cap, is spaced inwardly from the proximal end so that when the cap is positioned on the needle hub with the resilient bands in engagement with the stop bead, the lower end of the needle hub will be approximately aligned with the lower end of the cap. In addition, in the improvement, instead of having a single resilient band extending from each flap in one direction a little less than 180 degrees, two resilient bands extending in both circumferential directions from each flap for a little less than 90 degrees wherein four resilient bands are provided instead of two and the resilient bands are considerably shorter. By reducing the length of the bands to a little less than 90 degrees, the frictional force with which the bands engage the cap is made more nearly uniform from unit to unit, and as a result, the amount of force required to slide the cap on the needle hub assembly is made more nearly uniform in different manufactured units.
In another embodiment disclosed in U.S. Pat. No. 4,842,587, the flaps include portions extending radially beyond the resilient bands, and the cap defines channels for receiving the flaps. The channels widen abruptly, at their ends adjacent to the syringe, to define slots into which the radially extending portions of the flaps can be twisted to lock the cap in its extended position.